In order to achieve objectives for identifying and managing content and providing related information when distributing content such as the image, video and voice, there is a method using the digital watermarking technology for imperceptibly embedding another information into the content. Especially, for the usage in which a printed matter is input in a scanner or in a camera so as to detect digital watermark from the input image to provide related information (refer to non-patent document 1 and the like), a detection method that can perform processes at high speed is required for detecting the digital watermark in a terminal such as a mobile telephone that lacks enough computational resources.
Although geometric conversion caused by camera angle is corrected using a frame line and the like, and lens distortion is corrected using distortion coefficients determined beforehand (refer to the non-patent document 1), since an error may occur to some extent according to accuracy of correction, geometric distortion remains to some extent in an image from which the digital watermark is to be detected. Conventionally, as a digital watermark technology that has tolerance to such geometric distortion, there is a method disclosed in patent document 1.
However, in the conventional technology, there is no digital watermark embedding method and no detection method that can perform the detection process at high speed in a terminal while allowing some geometric distortion.
[Non-patent Document 1]                Nakamura, Katayama, Miyaji, Yamashita, Yamamuro “Digital watermark detection scheme for service mediation using mobile telephone with camera”, Forum on Information Technology FIT 2003, N-020, September 2003.        
[Patent Document 1]                Japanese Laid-Open Patent Application No. 2000-287073        